HR: 17:00h
AN: V54B-05    [Abstracts]
TI: Evolution from Oceanic Subduction to Continental Collision: A Case Study of the Northern Qaidam UHP belt
AU: * Zhang, L
EM: Lfzhang@pku.edu.cn
AF: Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, Beijing, 100871
AU: Song, S
EM: sgs@pku.edu.cn
AF: Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, Beijing, 100871
AU: Niu, Y
V54B-05 AF: Geologic Lab Centre, Chinese University Of Geosciences, Beijing 100083, Beijing, 100083
AU: Song, B
V54B-05 AF: Department of Earth Science, Durham University, Durham Dh1 3le, UK, Durham, Dh1 3LE
AU: Liu, D
V54B-05 AF: Department of Earth Science, Durham University, Durham Dh1 3le, UK, Durham, Dh1 3LE
AU: Su, L
V54B-05 AF: Shrimp Laboratory, Institute Of Geology, CAGS, Beijing 100037, Beijing, 100037
AB: Two apparently distinct paleo-subduction zones are recognized in parallel along in the northern margin of the Tibetan Plateau: the North Qilian Oceanic-type Suture Zone with ophiolitic m"Ýlanges and high-pressure eclogite and blueschist in the north, and the North Qaidam Continental-type Belt in the south with ultrahigh-pressure (UHP) metamorphic terranes comprising pelitic and granitic gneisses, eclogite and garnet-peridotite. Eclogites from both belts have protoliths broadly similar to MORB or OIB with overlapping metamorphic ages (480"C440 Ma, with weighted mean ages of 464­A6 Ma for the North Qilian and 457­A7 Ma for the North Qaidam) by zircon U-Pb SHRIMP dating. Coesite-bearing zircon grains in pelitic gneisses from the North Qaidam UHP Belt yield a peak metamorphic age of 423­A6 Ma, 40 Myrs younger than eclogite formation. This age records a geologically significant event of UHP metamorphism in the Norhern Qaidam and is consistent with the peak metamorphic ages of garnet lherzolite (423­A5 Ma) and garnet-bearing dunite (420­A5 Ma) in the same belt (Song et al., EPSL, 2005). These zircons also recorded a retrograde age of 403­A9 Ma, the same as retrograde ages of garnet peridotite. These data, combined with regional relationships, allow us to infer that these two parallel belts may represent an evolution sequence from oceanic subduction, to continental collision, to continental underthrusting and to the ultimate exhumation. The Qilian-Qaidam Craton was probably a fragment of the Rodinian super-continent with a passive margin and extended oceanic lithosphere in the north, subducted beneath the North China Craton to depths greater than 100 km at ca. 423 Ma and exhumed at ca. 403 Ma (zircon rim ages in pelitic gneiss).
DE: 1100 GEOCHRONOLOGY
DE: 3654 Ultra-high pressure metamorphism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005